Adding operator to the toolshelf?
To add it it to the toolbar, simply have your class inherit from bpy.types.Panel, and call the class functions, the key one being draw(). You choose a space_type, a region_type and the context in which the panel should be shown. 

You can also reference the example below the one you are using. BlenderCookie also has a tutorial that covers this.

See the modified code

import bpy

class SimplePanel(bpy.types.Panel):
    bl_id_name = "object.simple_operator"
    bl_space_type = "VIEW_3D"
    bl_region_type = "TOOLS"
    bl_context = "objectmode"
    bl_label = "Simple Panel"

    def draw(self, context):
        layout = self.layout
        col = layout.column(align=True)

        col.label(text="Objects in the scene:")

        col2 = layout.column(align=True)
        for ob in context.scene.objects:
            col2.label(text=str(ob.name))

def register():
    bpy.utils.register_class(SimplePanel)

def unregister():
    bpy.utils.unregister_class(SimplePanel)

if __name__ == "__main__":
    register()